Apparatus for the simultaneous transmission of telephonic and telegraphic currents over the same line.



110.801,936. PATENTED OCT. 1'7, 1905. C. TURGHI.

APPARATUS POR THE SIMULTANBOUS TRANSMISSION 0F TBLEPHONIG ANDTELBGRAPHIC CURRBNTS OVER THE SAME LINE.

APPLIOATWN FILED JULY 13,1904.

A Fi A. A.

@ NR 1m "321% gf NJW? w Unes@ UNITED sTATEs PATENT` FFIQB.

CARLO TURCHI, OF FERRARA, ITALY.

APPARATUS FOR THE SIMULTANEOUS TRANSMISSION OF TELEPHONIC ANDTELEGRAPHIC CURRENTS OVER THE SAME LINE.

Specification of Letters Patent.

Patented Oct. 17, 1905.

Application iiled July 13, 1904. Serial No. 216,374.

Toni/Z whom it may concern:

Be it known that I, CARLO Tnonnengineer, a subject of the King of Italy,anda resident of Ferrara, in the Kingdom of Italy, have invented certainnew and useful Improvements in Apparatus for the SimultaneousTransmission ot' Telephonic and Telegraphic Currents Over the Same Line;and I do hereby declare the following to be a `full, clear, and exactdescription of the invention,such as will enable others skilled in theart'to which it appertains to make and use the same, reference being hadto the accompanying drawings, and to letters of reference markedthereon, which form a part of this specification.

My invention relates to enable a double metallic telephone-line e. atelephone-line composed of a wire for the outgoing and a second parallelwire for the return current) to be used eiTectively and advantageouslyas a conductor for the simultaneous transmission of a telephonic currentwith another current, hereinafter called the superimposed current,77without interference between the two currents. The superimposed currentmay be atelephonic, telegraphic, or high-potential continuous oralternating current. Some solutions of this problem have already beengiven by Ducousso, Pierard, Caihlo, Swensky, Barret, Jacob, and Gaunt;but my present invention provides a new solution and is able to obviatemany important practical diiiiculties presented more or less by theabove solutions.

Figure 1 is a diagrammatic view showing the ordinary system for thetransmission of simultaneous telephonic and telegraphic messages overthe same line. Fig. 2 is a diagrammatic view of a portion ot' my system.Fig. 3 is a longitudinal section through my separator-coil. Fig. I isadiagrammatic view showing a plurality of telephonic systems on a singlemetallic circuit.

In order to enable this invention to be clearly understood, I shallfirst proceed to describe its theoretical basis,which is common to theart, with reference to the diagram shown by Fig. l of the accompanyingdrawings. In this figure, A B and C D are the two linewires of atelephonic line with complete metallic circuit, and T' and T2 are thetwo telephonic terminals. The points A D at one end of the line areconnected to the conductor M H, and the points B and C at the other endI mission of spoken messages.

are connected to the conductor N K. The conductors M H and N K areearthed at their ends H and K. I), situated between H and M, representsa generator of current-tele phonic, telegraphic, or high-potentialcontineous or alternating current--and Q, situated between K and Nrepresents an apparatus for receiving the current, which will reach thesaid receiving apparatus through the two wires of the telephonic line inparallel. In general a portion of the superimposed current will passthrough the telephones Tl and T2 and produce in them noises having amore or lessunfavorable influence on the etcient trans- In order toobviate such unfavorable inliuence, earlier inventors have proposed tomake the resistances of the branches MA M D equal and also to make thresistances of the branches B N and C N equal. By these means theelectrical potential is rendered equal at the points A D, and thereforeno portion of the current generated at P will flow through the branch AD and through the telephone T. Moreover', if the resistances of the twowiresA B C D are the same no portion of the said current will 'passthrough the branch B C and the tele no portion of the telephonic currentwill pass y through the conductor M IJ to earth, and likewise, for thesame reason, no portion of the telephonic current will flow through theconductor N Q to earth.

According to the foregoing general principle a double telephonic or theother line can be employed theoretically as a single conductor for asuperimposed current without interference between the two currents; butin practice the arrangement as described with reference to Fig. 1presents many weak points. First, the two wires of the telephonic linenever have exactly the same ohmic resistances, or if their ohmicresistances are exactly the same their respective impedances are notequal; second, the branches A M D and B N C act as short circuits forthe telephonic current, and thus considerably diminish the loudness ofthe transmitted voice.

Earlier inventors proposed various ways of providing the branches A M, MD, B N, C N with resistances in order to reduce so far as IOO possiblethe amount of the short-circuiting of the telephonic current through thebranches A M D and B N C. One inventor proposed an arrangement in whichthe impedances of the two telephonic lines were made as far as possibleequal to each other; but the introduction of resistance in the branchesA M, D M, B N, and C N necessarily diminished the strength of thesuperimposed current. Then some inventors proposed an inductivearrangement by which the resistance of the said branches to thesuperimposed current was practically unaltered, while the resistance tothe short-circuiting of the telephonic current was very much increased.

Having thus explained the theoretical basis (which is common to the art)of this invention, I shall now proceed to set forth the practicaldisadvantages of the previously-proposed systems.

The first point to be considered when a telephonic line with metallicreturn is to be employed for a simultaneous superimposed-current serviceis that there should not be the slightest loss in the telephoniccurrent. Therefore the resistance of the branches A M D B N C should bepractically equal to the insulation resistances.

Second. The introduction of such resistances in the branches A M, D M, BN, vC N should not cause the least loss in Athe superimposed current,especially if the latter is a telephonic current. s I

Third. The impedances of the two telephonic lines, as above stated, mustbe made equal, which they very seldom are in reality. Therefore thesystem must be provided with means for regulating the said impedances,and in order not to alter the resistance of the wires A B and C D, andthus produce a loss in the telephonic current, such means must beprovided in the-branches A M, D M, B N, C N.

Fourth. The electrostatic capacity between the branches A M and M D or BN and C N must be practically m'l, in which respect the earlier systemshave been chiefly deficient. Obviously the short-circuiting of thetelephonic current may take place not only through vthe ohmicresistances of the branches A M D and B N C, but also through the saidelectrostatic capacity, which in certain arrangements of theabove-described system is very great and is suiicient to cause a .greaty loss of telephonic current.

this figure the invention is assumed to be applied to a superimposedtelegraph service, but only by way of example. In fact, any othersuperimposed current may be employed. Referring now to the said iigure,Pis the Morse station, T the receiving-telephone, m the microphoneprovided with its battery p and its transformer t. The two branches M Aand M D are wound on one and the same soft-iron core in the followingway to form a separator coil. The two branches are wound together forthe greater part of their length, the remainder of the length of eachbeing wound as -a separate coil. Thus M A Y iirst is wound alone -for alength a b on the core S T, and then it is wound as to its remainder c Zon the same core together with the branch M D, as shown more clearly inFig. 3. Similarly, a portion cf of the branch M D is wound alone, andthe remainder g /L is wound together with M A.

So far as possible the coils ab and e f must be equal. The coils c CZand g /L being wound together are always exactly equal. Furthermore, thetwo branches M A and M D are wound in opposite directions, so that theyhave a differential action on the core S T.

The separate or additional coils or windings of the respective branchesAneed not necessarily be made as a whole with the main winding, asdescribed and shown, but they may be separate therefrom.

The ohmic resistances of the branches M A M D are exactly equal, andtheir inductances are made exactly equal by a very simple arrangement ofregulation. The length of the core S T is shown exactly equal to thedistance af, so that if, for instance, the inductance of the branch M Ashould be greater than the inductance of the branch M D the core S Tmust be shifted by suitable means, such as a screw, to the right. As theinductance of the branch M D does not change while the inductance of thebranch M A is lessened, it is obvious that the two inductances can bemade exactly equal. shorter than the distance a f-for instance, asindicated by the dotted lines 1/ in Fig. 3-in which case by acting byits movement in oppositew'ay on the two branches the regulation will berendered more delicate. Thu's by this means of regulation the impedancesof the two branches A M D M are rendered exactly equal. 1f now atelegraphic current is generated by the apparatus P,'this current willdivide in two parts, each of which will iiow through one of thebranches, as indicated bythe black arrows, and as the impedances of thetwo branches aremade equal and the Abranches are Wound in oppositedirection, the self-inductance introduced inthe telegraphic circuit bythe above system will be exactly m'l, so that the only alteration in thetele- Cgraphic circuit will consist in the increase of the ohmicresistance, which will be equal to IOO IIO

The core S T might be made IZO ISO

one-half of the ohmic resistance of one of the branches. Thus whatevertelegraphic system-simplex or duplex or quadruplexwmay be used its speedwill never be reduced.

The result of regulating the branches A M D M, as above described, so asto obtain the same potential at the points A and D is that no portion ofthe telegraph-current will Aflow through the branch A D and thetelephone T will be silent.

The case of a telephonic current flowing through the telephonic circuitwill now be considered. Itis assumed that the telephonic current isproduced by the microphone m and passes through the transformer tto thebranch A D, and thus to the line. A portion of this current will flowthrough the branch A M D; but as the impedances of the 'branches A M D Mare equal no telephonic current will go to earth through M P H. Thedirection of the current in the derivation A M D, as indicated by thedotted arrows, is such that the inductances of the two branches areadded together, and as the mutual inductance between the two branches ispractically equal to the self-inductance of one of them, according tothe construction of the coil, it can be assumed that the current willflow through a circuit the inductance of which is four times theinductance of one of the branches.

Now since, as above stated, the inductances of the two branchesneutralize each other with respect to the superimposed circuit, therewill be no difficulty in selecting the self-inductance of each branch insuch a way that the four times greater inductance which the currentfinds in the circuit A M D will act practically as an insulationresistance, so that the loss of the telephonic current through theshunt-circuit is thus rendered practically m'l.

Expressed in figures, the improved apparatus offers to the telephoniccurrent in the circuit A M D an impedance of about three hundred andtwenty thousand ohms, while only an additional resistance of eighty ohmsis offered to the superimposed telegraphic current.

In order to prevent loss due to the circumstance that the electrostaticcapacity between the two branches may be great enough to allow aconsiderable portion of the current to pass from one branch to theother, the coil is wound as shown 4in Fig. 3. which shows the twoadditional small coils a e f, used for the regulating device, wound inseparate places a b c f and the coils c Z g /t wound together in thecentral part of the coil /i t.

The wire of the branch A M is representedY by white circles and the wireof the branch D M by hatched circles.

In the ligure the wires of the two branches are shown alternating ineach row. Care is also taken that under a convolution of the wire of onebranch there is situated a convolution of the wire of the other branch.The electrostatic capacity between the two branches could eXistin twoways: first, by considering each horizontal row as a face of acylindrical condenser, and, second, by consid- V the two rowsp gu/ q g',each face of such a condenser is neutral, and if also the number of therows is even the total capacity of the horizontal rows is m'l.Similarly, if two sections, such as man n, n', be considered, the numberof the rows being even, then both faces of such acondenser will beneutral, and therefore, the number of the convolutions being even, thetotal capacity of the sections will be also m'l. Therefore there will beno loss whatever of the telephonic current, while any rapid telegraphicsystem may be used as the superimposed circuit.

lf, as is usually the case, the-impedances of the two wires of thetelephonic line are not equal,they may bemade equal by the regulation ofthe impedances of the branches M A M D and there will be no loss oftelephonic current through M H to earth, because of the high impedanceof the derivation A M D, as above set forth.

This invention may be applied to various purposes: first, forsuperimposed telegraphic, telephonic, orhigh-potential currents; second,for combined telephone-circuits, which problem is too well known to needdescription;

third, in combination with a system of simul.

taneous telephony and lgelegraphy, the apparatus for which canbeincluded in the conductors M H and N K, thus giving three superimposedelectrical communications. If the telephone-line in any of such cases isdivided in various branches, each of them must be provided at each endwith such a separatorcoil in the manner shown in diagram in Fig. 4. Inthis figure the telephone-line is shown divided. in three sections, ateach end of which are placed the separator-coils A Ab AC A1 Ae Af. Thetelephonic stations are represented by Ta Tl Tc Td Te Tf. vThe currentproduced by the generator P will first iiow through the telephonicsection T Tb, and as the separator-coils must be regulated nodisturbances will be produced in the telephones of said section. Then,if the vertex N of the separator of the endB of the first section isconnected to the verteX R of the separator ofv the end C of the secondsection, the superimposed current will iiow through the secondtelephonic section in a similar manner without disturbing the telephonesTe Td, and similarly the third telephonic section will be connectedthrough the conductor S T, thus the superimposed current reaching thereceiving apparatus Q without having given any rise to disturbances inthe telephones of the three sections, which will remain quiteindependent one from the other.

IOO

One could easily understand how to proceed if instead of having threetelephonic sections their number would have been four, five,

or any number. Y

Having thus described my invention, what I claim as new, and desire tosecure by Letters Patent of the United States of America, is-

l. In a superimposed telegraph and telephone system,the combination witha doublemetallic telephone-line and its telephonic apparatus, of aseparator coil bridged across the two line-wires, comprising two coilsof equal inductance wound together in opposite directions on the samecore, and a telegraph branch circuit with telegraphic apparatus leadingfrom a point of the separatorcoil chosen between its two coils, theseparator-coil being so constructed as to present no inductiveresistance to the telegraph-current and an extremely high impedance tothe telephone-current, as hereinbei'ore described.

2. In a superimposed telegraph and telephone system,the combination witha doublemetallic telephone-:line and its telephonic apparatus, of aseparator-coil comprising two branches coiled together and separately onthe same core, the inductances of the two branches being made equal bymeans of regulation, and a telegraph branch circuit and its telegraphicapparatus leading to earth from a point of the separator-coil chosenbetween its two branches, the separator-coil being so constructed as topresent no inductive resistance to the telegraphic current and anextremely high impedance to the telephone-current, as hereinbeforedescribed.

3. In a superimposed telegraph and telephone system, the combinationwith a double-metallic telephone-line and telephone apparatus, of a"separator-coil7 bridged across the two line-wires, comprising twobranches wound together in opposite directions on the same core, and twoadditional coils inserted in each one of the said branches, and amovable core, around which the two branches and the two additional coilsare Wound, the inductances of the two branches being made equal bysuitably adjusting the movable core, and a branch telegraph-circuitprovided with telegraph apparatus, leading to earth from a point of theseparator-coil chosen between the two branches, the separator-coil beingso constructed as to present no inductive resistance to the telegraphiccurrent and an extremely high impedance to the telephone-current, ashereinbefore described.

4. In a superimposed telegraph and telephone system the combination witha double-metallic telephone-line,and telephone apparatus, of a separatorconnected across the two line-wires, comprising two branches woundtogether in opposite directions on the same core, in such a way that theelectrostatic capacity between the two branches is m'l, and twoadditional coils inserted in each one of the branches, and a movablecore, the latter and the additional coils forming a means of regulationby which the inductances of the two branches and of the two line-wiresare made equal, and a branch telegraph-circuit' with telegraphicapparatus leading to earth from a point of the separator-coil chosenbetween the two branches, the separator-coil being so constructed andadjusted as to present no inductive resistance to the telegraphiccurrent and an extremely high impedance to the telephone-current ashereinbefore described.

5. In a superimposed telegraph and telephone system, the combinationwith a double-metallic telephone-line and its telephonic apparatus; of aseparator-coil bridged across the two lines and comprising a core, andtwo branches wound together on the core into a coil with an even numberof rows and an even number of sections, the wires of the branchesalternating in each row and in each section; and a` telegraph branchcircuitfwith a telegraphic apparatus, leading from a point of theseparator-coil between its two branches.

6. In a superimposed telegraph and telephone system, the combinationwith a double-metallic telephone-line and its telephone apparatus; of aseparator-coil bridged across the two lines and comprising a movablecore, and two branches wound together and separately about the movablecore; and a telegraphic branch leading from a point between the twobranches.

7 The combination with a plurality of double-metallic telephone mainlines and their telephonic apparatuses; of a separator-coil bridgedacross each main line at both ends thereof and comprising a core, andtwo branches wound together about the core in opposite directions; andtelephone branches leading from a point between each branch of theseparator.

The foregoing specication signed at Venice, Italy, this 7th day of June,1904.

CARLO TURCHI. In presence of- KARL FRANKE, RoBT. W. BLIss, ALPHoNsPRANTOR.

IOO

